The Supreme Court on Monday will hear oral argument in a case called Friedrichs v. California Teachers Association. It’s one of the most hotly contested disputes of the court’s 2015-16 term, with serious stakes for law, politics and business.

It raises lots of questions; here are some of them.

Q: Who is Friedrichs, and what’s her complaint against the California Teachers Association?

A: Rebecca Friedrichs is a longtime elementary school teacher in Orange County. Along with San Luis Obispo County teacher Irene Zavala, Harlan Elrich, a math teacher at Sanger High School near Fresno, and others, Friedrichs objects to mandatory fees charged by a teachers association to which they do not belong.

These fees add up. In 2013, the California Teachers Association collected $173.9 million in what Friedrichs’ attorneys characterized as “dues.” California teachers say their individual fees can exceed $1,000 a year.

Q: Is money the only issue?

A: It’s more than that. The teachers say they don’t want to underwrite union activities that are contrary to their beliefs. Forcing them to pay, they say, violates their First Amendment rights; the constitutional provision that they argue empowers people both to speak and, if they choose, not to speak.

Elrich said in an interview that “a lot of money is being taken from me to support bills and candidates I don’t support.” Zavala, though allowed for religious reasons to donate her agency fee to charity, contended in a legal brief that her “charitable contributions are constrained by a collective-bargaining agreement” and added that she objects to “many of the unions’ public policy positions.”

But for California’s agency shop arrangement, Mr. Elrich would not pay fees to or otherwise subsidize the teachers’ union, and he objects to the state’s forced subsidization policy. Brief for Fresno-area teacher Harlan Elrich and others.

Q: Is this only about teachers?

A: It just starts there. About 7.2 million public-sector employees belong to unions nationwide, and a brief led by Stanford Law School professor Pamela S. Karlan for the Peace Officers Research Association of California noted that “these members worked in diverse occupations, including library services, health care, job training and more.”